Introduction to Virtual Machines

Transcription

1 Introduction to Virtual Machines abstraction and interfaces virtualization Vs. abstraction computer system architecture process virtual machines system virtual machines

2 Abstraction Abstraction is a mechanism to manage complexity in computer systems. Mechanism consists of partition the design of a system into levels allow higher levels to ignore the implementation details of lower levels In computer systems, lower levels are implemented in hardware, and higher levels in software.

3 Interfaces An interface defines the communication boundary between two entities. Allows de coupling of computer design tasks each component provides an abstraction of itself to the outside world Advantages work on different components can progress independently helps manage system complexity Drawbacks tying down the interface limits later system flexibility

4 Virtualization Virtualization constructs an isomorphism that maps a virtual guest system to a real host. See figure 1.2 Virtualization Vs. abstraction virtualization does not necessarily hide details See figure 1.3

5 Virtual Machines A virtual machine is implemented by adding a layer of software to a real machine to support the desired virtual machine s architecture. Virtualization mapping of virtual resources or state to real resources use of real machine instructions to carry out actions specified by the virtual machine instructions

6 Some Benefits of VMs Flexibility Portability Isolation Security

7 Computer System Architectures Architecture functionality and appearance of a computer system, but not the details of its implementation Implementation the actual embodiment of an architecture See Figure 1.4

8 Machine Interfaces process perspective ABI provides the interface between the process and the machine. See Figure 1.5a system perspective ISA provides the interface between the system and the machine. See figure 1.5b

9 Process Virtual Machine Process virtual machine is capable of supporting an individual process. See Figure 1.6

10 System Virtual Machine System Virtual Machine is capable of supporting an OS along with potentially many user processes. See Figure 1.7

11 PVM Multiprogramming PVM provided by a multi process OS for each concurrently executing application. Combination of the OS system call interface, and the user level ISA. Each process is given the illusion of having the complete machine to itself.

12 PVM Emulators Execute binaries compiled to a different instruction set than that executed by the host s hardware. Interpretation low startup overhead high steady state per instruction emulation overhead

13 PVM Dynamic Translators Run time translation of blocks of source instructions to equivalent target instructions. high start up translation overhead fast steady state execution Uses a code cache to store translated blocks of code for reuse. e.g., Digital s FX!32 system, Aries system, Intel IA 32 EL system

14 PVM Same ISA Binary Optimizers VMs where the source and target ISAs are the same. Main task is the optimization of the source binary may also collect performance profiles may also enhance security e.g., Dynamo system, developed at Hewlett Packard.

15 PVM High Level Language VM A HLL is designed with the goal of being executed in a VM. minimize hardware specific and OS specific features that could compromise portability earlier program distribution than in conventional system, see Figure 1.10 e.g., Java VM architecture, Microsoft common language infrastructure (CLI)

16 Classic System Virtual Machine Original meaning of the term virtual machine all guest and host software use the same ISA See Figure 1.11 VMM runs on the bare hardware most privileged mode VMM intercepts and implements all the privileged operations for the guest OS.

17 Hosted System Virtual Machine Virtualizing software is built on top of an existing host OS. Advantages installation is like installing application programs host OS provides device driver support Drawbacks less efficient

18 Whole System VMs Different ISA for guest and host systems. both application and OS code require emulation Implemented by placing the VMM and the guest software on top of a conventional host OS running on the hardware see Figure 1.12 e.g., Virtual PC

19 Codesigned Virtual Machines VMs designed to enable innovative ISAs and/or hardware implementations for improved performance, power efficiency, etc. Similar hardware virtualization is common for microprocessors, such as Pentium IV. Software VM is part of the hardware design applications/os never directly execute native ISA instructions e.g., Transmeta Crusoe processor

20 see Figure 1.13 VM Taxonomy